A person says "Inshallah I will do this", and then he does not do what he said he would do. Now he says that his statement "Inshallah I will do this" remains true because the word "Inshallah" specifies the will of Allah, and his not doing it means that Allah did not wish for it to happen, and as he included this condition, i.e. the word "Inshallah" in his statement, so his not doing it does not make him a liar. Is this person right?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His Slave and Messenger.

A Muslim should not say his intention to do something or promise to do it without saying Inshaa’ Allaah (if Allaah wills), because Allaah The Exalted says (what means): {And never say of anything, "Indeed, I will do that tomorrow"/Except (when adding), "If Allaah wills".} [Quran 18:23-24] However, one should not say his intention to do something or promise to do it saying "If Allaah wills" if he is lying and intends to break that promise. Saying Inshaa' Allaah in this case does not change the fact that such an action is considered a lie and an intentional breach of promise.

Ibn Rajab said: “When one makes a promise intending to break it, this is the worst form of breaking the promise. When one proclaims his intention to do a certain act and says "I will do such an act, if Allaah wills," while intending not to do it, such an act constitutes both lying and breaking the promise, as Al-Awzaaʻi said.”

On the other hand, when one says his intention to do something while intending to do it and says "If Allaah wills," this is the prescribed thing to do in this regard. If he is unable to do what he intended to do, by the Will of Allaah, he is not to be blamed for it and he bears no sin for that. This would indicate that Allaah has willed and decreed that such a thing should not take place.

Allaah Knows best.